The present invention relates to an airbag system for securing the safety of an occupant of a vehicle by deploying an airbag when the vehicle is involved in a collision or the like, and more particularly to an airbag system which includes a communication unit which makes up a network together with other electronic control units within the vehicle.
A controller area network (hereinafter, referred to as CAN) is a seal bus system which is standardized for vehicles for interchanging information and data between a plurality of electronic control units (hereinafter, referred to as ECU). A CAN driver which controls a CAN communication is normally provided as an independent IC, which is incorporated in an ECU for airbags or the like as an independent part for use. However, CAN driver IC's themselves are expensive and therefore constitute one of main causes for an increase in the ECU cost. Due to this, it has been desired that a CAN driver is incorporated in a single integrated circuit together with other electronic units in the ECU so as to make up an ASIC, whereby the necessity of an independent CAN driver IC is obviated to realize a reduction in the ECU cost.
A CAN driver IC is disclosed in, for example, Japanese Patent Publication No. P10-105309, and the incorporation of a CAN driver in an ASIC is disclosed in, for example, Japanese Patent Publication No. P2004-286029.
FIG. 1 shows the configuration of a related-art airbag ECU in which a CAN driver is incorporated. An airbag ECU 100 includes a main G-sensor (an acceleration sensor) 1 for detecting a collision of a vehicle, a safety G-sensor 2, a microcomputer (hereinafter, referred to as a main microcomputer) 3 for determining on a colliding state in software based on an output of the main G-sensor, a microcomputer (hereinafter, referred to as a sub-microcomputer) 4 for performing a safety collision determination in software based on an output of the safety G sensor 2 and output circuits 5 (5a, 5b, . . . , 5n) for outputting airbag ignition signals based on a collision determination signal from the main microcomputer 3 and a safety determination signal from the sub-microcomputer 4. The output circuits 5 outputs a driving signal to airbags 6 (6a, 6b, . . . , 6n) which is mounted on the vehicle. Each of the airbags 6 includes a squib (not shown) for exploding by being electrically connected so that the airbag is deployed, and a switching transistor (not shown) for controlling supply of power to the squib. A system power supply circuit 7 supplies power to the squib. The output circuits 5 are connected to a base of the switching transistor. In a case where the output circuits 5 outputs the airbag ignition signals, the switching transistor is turned on and power is supplied to the squib.
Normally, the output circuits 5 are incorporated in a single IC as an ASIC 8 together with a power supply circuit (hereinafter, referred to as a system power supply circuit) 7 which forms a voltage needed to drive individual parts within the airbag ECU from an outside power supply.
The system power supply circuit 7 receives the supply of power by being connected to an onboard batter 10 via an ignition switch and forms a voltage which is necessary to drive the output circuits, the main microcomputer, the sub-microcomputer and the like. Furthermore, the system power supply circuit 7 is connected to a capacitor 11 which functions as a backup power supply and charges the capacitor 11 while power is being supplied thereto from the onboard battery 10, so that when the ignition switch 9 is turned off to thereby stop the supply of power from the onboard battery 10 to the system power supply circuit 7, the capacitor 11 supplies power to the system power supply circuit 7.
The airbag ECU 100 needs to operate properly to deploy the airbags, for example, even when the ignition switch 9 becomes off due to the vehicle being involved in a collision, whereby no power is supplied to the system power supply system 7 from the onboard battery. The backup power supply is such as to be provided to supply power that is necessary for the whole system in such a case.
The airbag ECU 100 includes further an input circuit 12 and inputs outputs from other acceleration sensors 13, 14 which are provided outside the ECU 100 into the main microcomputer 3 and the sub-microcomputer 4 via the input circuit 12. The acceleration sensors 13 are, for example, front sensors for frontal collision which are provided at the front of a vehicle body to detect a frontal collision, and the acceleration sensors 14 are satellite sensors for side collision which are provided on sides of the vehicle body to detect a side collision.
The airbag ECU 100 includes further a CAN driver 15 for performing a CAN communication between the main microcomputer 3 and other outside ECU's such as an electronic fuel injection (hereinafter, referred to as EFI) ECU 200 and a door ECU 300. The CAN driver 15 is provided as an single independent IC. As is described above, since the airbag ECU 100 needs to operate properly even when the outside power supply is cut off, the airbag ECU 100 has the backup power supply, but the CAN driver 15 does not have to continue to operate any longer when the outside power supply is cut off. Due to this, in the event that the system power supply is also used as a power supply for the CAN driver 15, it results that the CAN driver 15 continues to consume current from the backup power supply when the outside power supply is cut off. When the backup power supply is consumed by the CAN driver 15, the backup power supply needs to be configured by a capacitor having a large capacity, and this not only affects badly the miniaturization of the airbag ECU 100 but also constitutes one of main causes of an increase in costs.
Consequently, a power supply for the CAN driver 15 is provided as a separate line in the airbag ECU 100 so that the supply of power to the CAN driver 15 is stopped in the event that the ignition switch 9 becomes off. Reference numeral 16 denotes a power supply circuit for supplying a drive power to the CAN driver 15 (a CAN driver power supply circuit), and a commercially available power supply IC is used for this.
As described above, in the related-art airbag system, in order to secure the necessary backup power supply, the power supply for the communication unit such as the CAN driver needed to be provided as the separate line from the power supply for the airbag system. Due to this, in order to incorporate the communication unit in the processing circuit which outputs an airbag deployment signal, a separate power supply circuit which is connected to the outside power supply by way of a separate line from the power supply circuit for the airbag system, and this complicates the construction of the whole power supply circuit, and in order to realize such a power supply circuit, an IC chip having a large area is necessary. As a result, even in the event that the communication unit, which is configured by the independent IC is incorporated in the processing circuit to omit the communication IC, there still remains a problem that an extensive cost reduction cannot be expected as the whole airbag system.